Why don't turtles still have tail spikes?

We're all familiar with those awesome armored giants of the Jurassic and Cretaceous periods - Stegosaurus and Ankylosaurus - and their amazing, weaponized tails. But why aren't similar weaponized tails found in animals living today? In a study covering 300 million years of evolutionary history, researchers from North Carolina State University and the North Carolina Museum of Natural Sciences found four necessary components to tail weapon development: size, armor, herbivory and thoracic stiffness.

"Weapons like tail clubs and bony spikes are found only in a few extinct animals - such as ankylosaurs, glyptodonts (large extinct armadillos) and in some ancient turtle species," says Victoria Arbour, former postdoctoral student at NC State, current postdoctoral fellow at the Royal Ontario Museum and corresponding author of a paper describing the research. "These same weapons just don't occur in modern-day animals, and we wanted to know why they were so rare even in the fossil record."

Study co-author Lindsay Zanno, professor of biological sciences at NC State and head of paleontology at the NC Museum of Natural Sciences, agrees, "We kicked off this study with a simple observation: most animal weapons used for combat are located on the most critical part of the body for survival, the head, as opposed to more expendable ones such as the tail. Why, we asked, wasn't evolution producing more animals with weaponized tails, when this would seem to be far less dangerous?"

To answer this question, Arbour and Zanno looked at a data set of 286 amniote species, both living and extinct, to see if there were patterns that pointed to the evolution of three specific types of tail weapons: bony spikes, a stiff tail or a bony knob at the tip of the tail. Amniotes refer to backboned, four-legged reptiles and mammals, as well as birds.

In the case of bony tail weaponry, the researchers found the animals had four things in common. First, they were usually large, weighing over 200 pounds (or 100 kilograms) - about the weight of the glyptodonts that used to roam South America or a living mountain goat - or were over three feet (a meter) long.

Second, armor was key. Ancient turtles, armadillos and armored dinosaurs were covered in some sort of hard carapace or bony plated armor. Thoracic stiffness - referring to a body that doesn't bend side to side easily, perhaps so that it could easily counteract the forces needed to swing a large clubbed or spiked tail - was also important. Finally, every animal in the fossil record that developed elaborate tail weaponry was an herbivore, or vegetarian.

"It's rare for large herbivores to have lots of bony armor to begin with," Arbour says, "and even rarer to see armored species with elaborate head or tail ornamentation because of the energy cost to the animal. The evolution of tail weaponry in Ankylosaurus and Stegosaurus required a 'perfect storm' of traits that aren't seen in living animals, and this unique combination explains why tail weaponry is rare even in the fossil record."

Zanno continues, "This study is an elegant example of how the fossil record can be used to better understand the world around us today."

Related Stories

How did the ankylosaur get its tail club? According to research from North Carolina State University and the North Carolina Museum of Natural Sciences that traces the evolution of the ankylosaur's distinctive tail, the handle ...

Ancient dinosaurs were adorned in some amazing ways, from the horns of the triceratops to the plates and spikes of the stegosaurus. A newly discovered, bird-like dinosaur fossil from China contains evidence that could add ...

A wagging tail is often associated with dogs' emotions, but the side-to-side motion may also help them take longer strides and move faster, according to a study by researchers at the University of California, Riverside.

(PhysOrg.com) -- Scientists in Uruguay studying extinct mammals called glyptodonts have discovered they used a "sweet spot" in their tails, just like baseball players use the center of percussion (CP), or sweet spot, in their ...

Just when dinosaur researchers thought they had a thorough knowledge of ankylosaurs, a family of squat, armour plated, plant eaters, along comes University of Alberta graduate student, Victoria Arbour.

Using modern research tools on a 155-million-year-old reptile fossil, scientists at Johns Hopkins and the American Museum of Natural History report they have filled in some important clues to the evolution of animals that ...

Young mongooses learn lifelong habits from role models rather than inheriting them from genetic parents, new research shows.Banded mongooses live in social groups where pups are consistently cared for one-to-one by a single ...

Although evolution has left dragonflies virtually unchanged for roughly 300 million years, new research by a UTM biologist reveals that understanding small physiological activities in these insects could reveal a deeper understanding ...

A large international team of researchers has found a link between urbanization and changes in animal body size. In their paper published in the journal Nature, the group describes their study of animals living in both urban ...

In many animals, males pursue alternative tactics when competing for the fertilization of eggs. Some cichlid fishes from Lake Tanganyika breed in empty snail shells, which may select for extremely divergent mating tactics. ...

0 comments

Please sign in to add a comment.
Registration is free, and takes less than a minute.
Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.